I've been looking at the drawings for my UFH heating system - trying to make sure I have all the bits ready for our plumber/electrician - and it looks like we may need a relay of some sort.

We have two manifolds and each has it's own pump and mixer. When either of these pumps is running the boiler pump needs to run as well. A simple logic OR function.

In the world of plumbing is there a standard little black box you can buy to do this?

It's an OSMA system fed from a thermal store. We have two seperate manifolds (one per floor) each with it's own built in pump. OSMA say a seperate pump is needed to circulate the water around the store to manifold loop. If we wern't using a store this loop would be the boiler primary loop. Each manifold has a bypass on the front.

There is a wiring center for each manifold and it's pump but I can't see an output for the primary/third pump.

Each wiring center has a signal called "Boiler Enable". There is a drawing showing how to set up two manifolds and this shows them wired together and going off the page... but is this an input or an output? Is this used by the programmer to switch the manifolds on/off ? or is it used by the manifolds to call for heat?  

all UFH i have done has always been a manifold per floor. and on 1 larger house 2 on ground floor.

new house I did this year had 2 manifolds 1 upstairs 7 zones plus the hallway as a bypass zone upstairs 5 zones plus hallway utility room and cloak room on a bypass downstairs. this was a reasonably large house but not massive.

scotspark wrote on Nov 12^th, 2006, 2:02pm:


We're using two maifolds with 11 ports on each. I think we are using 10 out of the 11 on each. That's not 20 zones though as a few rooms need more than one loop - partly because of the distance from the manifolds and partly due to room size.

I've not had UFH before and was concerned that we might have a problem with one room too hot and the other too cold and not be able to solve it if they are on the same loop. With a rad system you can easily turn one down a bit. Anyway some loops got added to avoid that risk.

I normally work on NuHeat  which has a main distribution manifold (with pump and mixer valve) which then  feeds zone manifolds, the wiring centre I think has a max of 12 zones as you say zones & loops aren't the same thing. If you've had the system designed by the manufacturers then it should work well. ANyway if you've anymore questions just post again.

Scotspark were all these zones controlled by their own stats I think the biggest house I've done was a 6 bed 2 bath (+ensuites) place which had 6 zone stats covering 14 rooms + hall, utility & downstairs cloak.

One last question from me...

Does it matter what pressure the UFH loops are run at? I ask because the store  I'm using (DPS heatbank) is vented so the loops will be at low pressure - just a few meters head.